A tetrafluoroethylene/propylene type copolymer (hereinafter referred to also as a TFE/P copolymer) is used as a rubber material remarkably excellent in the heat resistance and chemical resistance in such a severe environment that ordinary rubber materials are not durable. However, the TFE/P copolymer is poor in the cross-linkability at the time of producing a rubber product. As a method for improvement, a method of carrying out heat treatment at a high temperature for a long time was proposed (e.g. Patent Document 1). However, by such a method, the productivity was inadequate, since it required heat treatment at a high temperature over a long time. Further, when a fluoroelastomer composition obtained by incorporating various blend materials to the heat-treated TFE/P type copolymer obtained by this production method, was molded by means of a mold and cross-linked, the cross-linkability was not necessarily adequate.
Accordingly, it has been desired to develop a production method of a cross-linkable fluoroelastomer more excellent in the productivity, whereby functional groups excellent in cross-linkability can be introduced into the fluoroelastomer with high efficiency.
Patent Document 1: JP-A-53-9848